Viruses and human cancer

The cause of hum an cancer is probably multifactorial and the role of viruses is unclear. The study of retroviruses has led to the identification of oncogenes responsible for transformation and tum or induction. Human viruses associated with malignancies include the JC virus (associated with progressive multifocal leukoencephalopathy) and some adenoviruses. No hum an malignancies have been associated with the latter group. A num ber of herpes viruses of lower animals have been associated with malignancies and herpes simplex virus type 2 has been associated with carcinoma of the cervix and vulva. The Epstein-B arr virus has been associated with Burkitt’s lymphoma and nasopharyngeal carcinoma. Some circumstantial evidence suggests that cytomegalovirus may be associated with Kaposi’s sarcoma among homosexuals. The hepatitis B virus (HBV) has been associated with hepatocellular carcinoma. The fullfillment of Koch’s postulates presents ethical problem s regarding man and proving the viral etiology of human malignancy. Social experim ents may elucidate some of these questions. An increase in venereal herpes should be associated with an increase in carcinoma of the cervix and use of the HBV vaccine in populations with high incidences of HBV carrier states should decrease the incidence of hepatocellular carcinoma. The investigation of the retroviruses though not establishing viruses as causing hum an malignancies at least will improve our understanding of the malignant process. T ha t a p a r tic u la r h u m an cancer is caused by a virus is yet to be proven. The cause of hum an cancer is probably m ultifac to ria l in th a t en v iro n m en ta l, physical, and chemical stimuli, with per­ haps specific genetic factors in the right combination, can bring about malignant changes.1516 22 If and how viruses or viral products play a role in the developm ent of hum an malignancy is under intense in­ vestigation. I t is well established that a num ber of viruses of lower animals are able to cause malignancies in the natural host or in o ther species.615 It would be ludicrous to expect that viruses do not play a role in the developm ent of hum an cancer. T he causal re la tio n sh ip b e tw een v i­ ruses and hum an cancer is difficult to es­ tablish and the fullfillment of Koch’s pos­ tulates to prove the infectious etiology of some cancers rem ains difficult if not im ­ p ossib le . In te n s iv e investig a tio n a t­ tem pting to dem onstrate the causal re ­